At first glance, it is little more than a massive mound of dirt -- a quiet spot on the banks of the Stono River, home to snakes and other critters.

Years ago, it was not nearly so peaceful.

In 1864, this earthworks was one of the last lines of defense protecting Charleston from a last-gasp Yankee invasion, subjected to days of shelling from Union gunboats. But it held, and U.S. forces were again denied control of James Island.

Battery Pringle is one of the lesser-known forts around Charleston, a relic of the Lost Cause that enjoys little of the historical import of Forts Sumter or Moultrie. But it was a crucial piece of Confederate Gen. P.G.T. Beauregard's Siege Line.

The earthen battery, built by slaves in less than three weeks, held off Union forces trying to invade Charleston by taking James and Johns islands. For 10 days in July 1864, this mound of dirt fended off ground troops and the U.S. Navy -- no easy feat, given that it was undermanned and many of the troops were so ill-equipped they didn't even have shoes.

Pringle sits on the Charleston Museum's Dill Sanctuary, and the museum is offering tours for a rare chance to see this remarkably well-preserved fort.

"We could probably have it ready to go in a couple of days," joked

Grahame Long, the museum's curator of history. "Actually, we're fairly certain this is a refitted British battery. Beauregard chose not to reinvent the wheel."

On most of these tours, the first question Long gets is something along the lines of: "Is this it?" They expect a structure like Moultrie, not rolling hills which form the walls of a working fort with parade ground, gun ports and a parapet. But in fact, many of the batteries and forts around Charleston during the Civil War were much like Pringle, and few of them exist anymore.

"Some of the batteries in the Charleston area have been bulldozed, and of course the ones on Morris Island have been washed away," said local Civil War historian Warren Ripley. "Battery Pringle saw a certain amount of action and it is in good condition, reasonably so. It's very good that the museum is preserving the battery and offering people a chance to see it."

The battery dates to August 1863. Morris Island was about to fall completely into the hands of Union troops and Beauregard was desperate to increase the defenses on James Island. The Union blockade of Charleston Harbor was doing little to deliver the city to Union troops and, as Long said, "They knew James Island was a side door into Charleston."

Beauregard ordered "new lines" on James Island by the end of the month, shortly after Union troops on Morris Island began shelling the city with the famous Swamp Angel gun.

Accounts suggest that 4,000 slaves were used to build the fort, which took about 20 days. It was named after Confederate Capt. Robert Pringle, one of many Southerners killed defending Battery Wagner in the battle of Morris Island.

The battery runs 360 feet along the riverbank, and the walls range from 7 to 12 feet high. These days it takes a little imagination to see it as it once was. The powder magazine, built into the walls of the battery, has collapsed, the parade ground is overgrown with weeds, and live oaks have sprouted from the parapet.

"People ask why we don't clear all this out, make it look more like it did back then," Long said. "This stuff probably saved it. It suffered very little erosion during Hugo."

Long's tour of Battery Pringle also includes a visit to Battery Tynes, another earthworks built a mile upstream to protect Battery Pringle's flank. It is even more overgrown, but just about as well-preserved -- right down to the moat that protected it. Together, the two batteries offer a good look at the fortifications that Southern troops used to defend the Lowcountry, and are perhaps the best examples of earthworks that still exist -- better than, say, the remains of the Tower Battery, or Fort Lamar, in Secessionville.

Ripley said that makes Battery Pringle an important Lowcountry landmark.

"It's part of Charleston history and American history that needs to be preserved," Ripley said.